A natural shoulder joint may undergo degenerative changes for a variety of reasons, for instance arthritis. Alternatively, a shoulder joint may be fractured or otherwise damaged by an external force. When a shoulder joint is sufficiently degenerated or damaged it may be necessary to replace the natural joint with a prosthetic shoulder joint. Conventional shoulder prostheses comprise a humeral prosthesis, optionally with a glenoid prosthesis. For total or reverse arthroplasty a glenoid component is implanted, however for hemiarthroplasty the humeral component articulates against the natural glenoid cavity.
When the upper extremity of the humerus is fractured, the humerus generally breaks into several pieces, typically three or four. In particular, for a four part fracture, the humeral head splits off at the level of the anatomical neck, the greater and lesser tuberosities are separated from the humerus shaft below the tuberosities and the tuberosities are separated from one another along the bicipetal groove. As there is no longer a blood supply to the humeral head necrosis may begin. For repair of a three-part or four-part fracture, where the blood supply to the humeral head is damaged, the humeral head is replaced, and the greater and lesser tuberosities are reattached to the humeral shaft. Typically, the humeral component of a shoulder prosthesis comprises a stem for insertion into a bore extending into the intramedullary canal of the humerus, generally along the longitudinal axis of the bone, and an articulation component, which may be a convex bearing head in the case of total arthroplasty or a concave cup in the case of reverse arthroplasty. Typically, the articulation component is coupled to a neck portion of the stem, which extends from the intramedullary canal at an inclined angle relative to the longitudinal axis of a distal portion of the stem in order to recreate the anatomy of the natural joint. Commonly, humeral stem prostheses are secured in position within the intramedullary bore using bone cement. Alternatively, the stem may be coated with a material which encourages bone growth to hold the stem in position, such as Porocoat® or hydroxyapatite. One such humeral stem prosthesis is commercially available from DePuy Orthopaedics, Inc under the trademark Global FX.
As an alternative to humeral stem implants, it is known to repair some types of proximal humeral fracture using an intramedullary nail extending along a bore formed within the intramedullary canal. Screws pass from outside of the humerus, through holes formed within the nail and into the humeral head and the tuberosities. This type of fixation also suffers from vascular damage in the intramedullary canal. Furthermore, a significant drawback is that because the humeral head is not replaced the nail must be inserted through a hole formed in the articular cartilage of the humeral head. A plug must be inserted into the hole to restore the bearing surface.
For the repair of fractures of the femoral neck it is known to provide a form of prosthesis generally known as a thrust plate prosthesis. One such form of thrust plate prosthesis is disclosed within PCT patent publication WO2007/024980-A2. The prosthesis comprises a plate portion to be attached to the lateral extemal surface of the proximal femur.
One issue in dealing with long-limb arthroplasty, is accommodating various anatomic sizes. This becomes even more of a challenge when the desired sizes of linking components that must engage and disengage and be mechanically stable. Also, surgeons desiring the ability to adjust intra-operatively creates additional issues as does the desire by surgeons to have infinite adjustability, not finite size offerings.
It is an object of embodiments of the present invention to obviate or mitigate one or more of the problems of the prior art, whether identified herein or elsewhere.